ATBECHDE....FRGB..ITLILUNLSE......................MDIM360 - Ver 2.5 (21 Aug 1997) 2100000/00166831EUROPEAN PATENT SPECIFICATIONB119880113EP84304607.9198407051986022119860911enenen198801131988021986010819860219880113198802198703174 4C 07C 118/00 A 4B 01J 37/02 B 4B 01J 23/48 B 4B 01J 23/50 BdeKatalysatorenImproved catalystfrCatalyseurEP-A- 0 000 602EP-A- 0 106 038GB-A- 912 636Carcia, Peter Francis2413 Sweetbriar RoadWilmington, DE 19810USHeinsohn, George Edward6 Gilmore LaneElkton, MD 21921USRao, Velliyur Nott Mallikarjuna1 Georgetown AvenueWilmington, DE 19809USE.I. DU PONT DE NEMOURS AND COMPANY0020058019.145-243ei du pontDU PONT DE NEMOURS AND COMPANY, E.I.PONT DE NEMOURS AND COMPANY, E.I. DUNEMOURS AND COMPANY, E.I. DU PONT DE1007 Market StreetWilmington Delaware 19898USWatkins, Arnold Jacket al00037381Frank B. Dehn & Co., European Patent Attorneys, 179 Queen Victoria StreetLondon EC4V 4ELGBATBECHDEFRGBITLILUNLSE19860108198602

The present invention relates to the production of isocyanates, preferably methyl isocyanate.

At present methyl isocyanate is produced in the U.S.A. by phosgenation of monomethylamine followed by decomposition of the resulting carbamoyl chloride to methyl isocyanate and hydrogen chloride.

U.S. 4,207,251 discloses the oxidation of N-alkylformamides to the corresponding isocyanates over precious metal catalysts including silver.

The present invention relates to an improved process of converting formamides of the formula R(NHCHO)n where R is an organic group and n is 1 or 2 to the corresponding isocyante over a silver or silver/gold catalyst wherein the silver or silver/gold is deposited by vapor deposition, e.g. by sputtering or ion plating, on an inert support. Such catalysts give a higher productivity of isocyanate. When measured as g of product/g of silver/hr, productivity increases by more than a factor of 50 as compared with conventional silver crystal or silver wool catalysts.

According to the present invention, there is thus provided a process for preparing an isocyanate corresponding to the formula

where R is an unsubstituted alkyl group, cycloalkyl group, aryl group, aralkyl group or alkaryl group containing not more than 18 carbon atoms, or one of said groups substituted with chlorine, fluorine, cyanogen, alkyl carbonyl or alkoxy carbonyl containing not more than 10 carbon atoms in the alkyl or alkoxy group and n is 1 or 2 which comprises contacting an N-monosubstituted formamide corresponding to the formula where R and n are defined as above in the gas phase with an oxygen-containing gas in the presence of a catalyst formed of a particulate, hard nonporous refractory support on which has been deposited by physical vapor deposition from 0.5-50% by weight silver or a silver/gold alloy.

The catalyst used in the present invention may be prepared by sputtering or ion plating silver/gold on an inert support. Generally the metal or metal alloy will comprise from 0.05-50 weight percent of the total catalyst composition. Generally the catalyst support will be a hard, nonporous refractory particulate material having a mean particle diameter in the range of from 0.1 micron to 0.5 centimeter. Generally the support should have a surface area below about 20 square meters per gram and preferably less than 3 square meters per gram. Generally the support will be a ceramic material. Alumina and silica are the preferred catalyst supports although other oxides such as ceria, yttria, zirconia or titanium can be used.

The catalysts of the invention were prepared by physical vapor deposition where evaporated metal was allowed to deposit on a silica support which was biased electrically or by RF sputtering. In the latter method, fused silica particles which pass a 0.595 mm [30 mesh (U.S. Sieve Series)] screen and are retained on a 0.297 mm [50 mesh (U.S. Sieve Series)] screen were distributed in several pyrex dishes on a rotating substrate table beneath a silver target or gold/silver target and coated with the metal or metals. The particulate substrates were periodically mixed outside the sputtering chamber to ensure uniformity.

Generally the process of the present invention is carried out at from 300-6000C with from 400-5000C being the preferred range. Under comparable conditions when using silver wool where it is possible to have hot spots, the catalysts of the invention offer a more uniform distribution of small amounts of the metal or metal alloy on the support which results in a higher selectivity to methyl isocyanate.

The reaction is carried out in the gas phase in the presence of an inert gas such as nitrogen, carbon dioxide, helium, neon, argon or xenon. Nitrogen is the preferred carrier gas because it is inexpensive, but helium is used in some of the Examples to facilitate product analysis by gas chromatography. Generally the proportion of methylformamide in the reaction mixture at the start should be from 0.1-40 volume percent. There should be oxygen present in the reaction mixture for carrying out the reaction. The amount of oxygen present in the feed to the reactor is generally from 0.1-20 volume percent.

The pressure used is not particularly critical and may be varied from <1 x 105 Pa to 1 x 106 Pa or higher. For operational reasons it is most preferred that the reaction be carried out at an absolute pressure of 1 atmosphere.

The present invention is applicable to N-monosubstituted formamides of the formula

where R is an unsubstituted alkyl group, cycloalkyl group, aryl group (preferably phenyl), aralkyl group or alkaryl group containing not more than 18 carbon atoms, or one of said groups substituted with chlorine, fluorine, cyanogen, alkyl carbonyl or alkoxy carbonyl containing not more than 10 carbon atoms in the alkyl or alkoxy group and n is 1 or 2.

Methyl isocyanate is used in the production of certain insecticides and nematicides including s-methyi-N-[(methylcarbamoyl)oxy] thioacetimidate (methomyl), an insecticide.

Examples

In each of the Examples the catalyst was charged to a "U" shaped quartz tube reactor which has a 12 mm outside diameter. The reactor was brought to temperature in a sand bath under a flow of inert carrier gas. When the desired temperature is reached, oxygen flow is initiated and after about 2 minutes the monomethylformamide is introduced with sufficient carrier gas to achieve the desired composition. Total flow is such that the nominal residence time in the catalyst bed is about 0.2 second. After allowing one hour for equilibrium to be reached, samples are periodically withdrawn for analysis. In Examples 1-4 the gas flows reported are as measured at 0°C and atmospheric pressure. Inert carrier gas and residual oxygen are excluded from the analysis and results are reported as molar percentages.

Example 1

Particulate silica or irregular shape which passes a 0.595 mm [30 mesh (U.S. Sieve Series)] screen and is retained on a 0.297 mm [50 mesh (U.S. Sieve Series)] screen is coated with 0.9 weight percent silver by ion plating to prepare the catalyst. The reactor is charged with 3.2 g of the catalyst and the bed heated to 470°C. Flows to the reactor are adjusted to 500 cc/minute of nitrogen, 20 cc/minute of oxygen and 5.76 ml/ hour of liquid monomethylformamide. After reaching equilibrium, analysis of the effluent stream indicates a 43% conversion of monomethylformamide and a 78% selectivity for methyl isocyanate. This is equivalent to a production rate of 58.3 g methyl isocyanate per gram of silver per hour.

Example 2

Particulate silica of irregular shape which passes a 0.595 mm [30 mesh (U.S. Sieve Series)] screen and is retained on a 0.297 mm [50 mesh (U.S. Sieve Series)] screen is sputter coated with 4 weight percent silver to prepare the catalyst. The reactor is charged with 3.2 g of the catalyst and the bed heated to 470°C. Flows to the reactor are adjusted to 500 cc/minute of helium, 25 cc/minute of oxygen and 5.76 ml/hour of monomethylformamide. After reaching equilibrium, analysis of the effluent stream indicates an 85% conversion of monomethylformamide and a 75% selectivity for methyl isocyanate. After 14 hours, both numbers begin to drop but then rise. After 30 hours of exposure, a conversion of 90% of monomethylformamide was achieved with 81% selectivity for methyl isocyanate. No further change in catalyst performance is noted during additional exposure. This is equivalent to a production rate of 25.3 g of methyl isocyanate per g of silver per hour.

Example 3

This Example is a comparison using silver crystals as the catalyst.

The reactor is charged with 8.45 g of silver crystals and heated to 470°C. Flows to the reactor are adjusted to 500 cc/minute of nitrogen, 20 cc/minute of oxygen and 5.76 ml/hour of liquid monomethylformamide. After reaching equilibrium, analysis indicates an 80% conversion of monomethylformamide and a 47% selectivity for methyl isocyanate. This is equivalent to a production rate of 0.2 g of methyl isocyanate per g of silver per hour.

Example 4

This Example is a comparison using silver wool as the catalyst.

The reactor is charged with 3.5 g of 0.03 mm O.D. silver wool and heated to 470°C. Flows to the reactor were adjusted to 500 cc/minute of helium, 25 cc/minute of oxygen and 5.76 ml/hour of liquid monomethylformamide. After reaching equilibrium, analysis indicated an 80% conversion of monomethylformamide and a 77% selectivity for methyl isocyanate. This is equivalent to a production rate of 1.0 g of methyl isocyanate per g of silver per hour.

Example 5

Example 1 was repeated with 37 cc/minute of monomethylformamide vapor, 25 cc/minute of oxygen from air and 475 cc/minute of nitrogen, fed as a mixture of air and nitrogen. Under these flow conditions two different sputter coated catalysts were evaluated at 470°C and 500°C. After reaching equilibrium the product from the reactor was bubbled into an aqueous solution of monomethylamine to trap the isocyanate as 1,3-dimethylurea which was isolated after removal of excess of the trapping medium. The trapping period in all cases was 120 minutes and the conversion of the formamide >90%. Results are summarized in Table I. The Ag/Au on Si02 catalyst used in Table I was cosputtered with silica onto a silica support.

The theoretical weight of urea for 100% conversion and 100% yield is 17.3 g.

 1. A process for preparing an isocyanate corresponding to the formula where R is an unsubstituted alkyl group, cycloalkyl group, aryl group, aralkyl group or alkaryl group containing not more than 18 carbon atoms, or one of said groups substituted with chlorine, fluorine, cyanogen, alkyl carbonyl or alkoxy carbonyl containing not more than 10 carbon atoms in the alkyl or alkoxy group and n is 1 or 2 which comprises contacting an N-monosubstituted formamide corresponding to the formula where R and n are defined as above in the gas phase with an oxygen-containing gas in the presence of a catalyst formed of a particulate, hard nonporous refractory support on which has been deposited by physical vapor deposition from 0.5-50% by weight silver or a silver/gold alloy. 2. A process as claimed in claim 1 wherein the N-monosubstituted formamide is a compound in which R is -CH3 and n is 1. 3. A process as claimed in claim 2 wherein the process is carried out at from 300-6000C using an inert carrier gas wherein 0.1-40 volume percent monomethylformamide is present in the feedstream to the reactor and from 0.1-20 volume percent oxygen is present in the feedstream to the reactor. 4. A process as claimed in any of the preceding claims wherein the catalyst support is a ceramic material. 5. A process as claimed in claim 4 wherein the catalyst support is silica or alumina. 6. A process as claimed in any of the preceding claims wherein the catalyst support has a mean particle diameter in the range of from 0.1 micron to 0.5 centimeter. 7. A process as claimed in any of the preceding claims wherein the catalyst support has a surface area below about 20 square meters per gram. 8. A process as claimed in claim 7 wherein the catalyst support has a surface area below about 3 square meters per gram. 9. A process as claimed in any of the preceding claims wherein the silver or silver/gold alloy is deposited on the support by sputtering or ion plating. 10. A process as claimed in any of the preceding claims wherein the oxygen-containing gas contains nitrogen as carrier gas. 11. A process as claimed in any of the preceding claims wherein the reaction is conducted in a quartz reactor. 1. Verfahren zur Herstellung eines Isocyanats, entsprechend der Formel worin R eine unsubstituierte Alkylgruppe, Cycloalkylgruppe, Arylgruppe, Aralkylgruppe oder Alkarylgruppe mit nicht mehr als 18 Kohlenstoffatomen oder eine dieser Gruppen, substituiert mit Chlor, Fluor, Cyanogen, Alkylcarbonyl oder Alkoxycarbonyl mit nicht mehr als 10 Kohlenstoffatomen in der Alkyl-oder Alkoxygruppe ist, und n 1 oder 2 ist, durch Inberührunbringen eines N-mono-substituierten Formamids entsprechend der Formel worin R und n wie oben definiert sind, in der Gasphase mit einem sauerstoffhaltigen Gas in Gegenwart eines Katalysators, gebildet aus einem feinteiligen, harten, nichtporösen, feuerfesten Träger, auf welchem mittels physikalischer Dampfniederschlagung 0,5 bis 50 Gew.-% Silber oder einer Silber/Gold-Legierung niedergeschlagen worden sind. 2. Verfahren, wie in Anspruch 1 beansprucht, worin das N-monosubstituierte Formamid eine Verbindung ist, in welcher R -CH3 und n 1 ist. 3. Verfahren, wie in Anspruch 2 beansprucht, worin das Verfahren bei 300 bis 600°C unter Verwendung eines inerten Trägergases, worin 0,1 bis 40 Vol.-% Monomethylformamid im Speisestrom in den Reaktor vorhanden sind und 0,1 bis 20 Vol.-% Sauerstoff im Speisestrom in den Reaktor vorhanden sind, durchgeführt wird. 4. Verfahren, wie in einem der vorstehenden Ansprüche beansprucht, worin der Katalysatorträger ein keramisches Material ist. 5. Verfahren, wie in Anspruch 4 beansprucht, worin der Katalysatorträger Siliciumdioxid oder Aluminiumoxid ist. 6. Verfahren, wie in einem der vorstehenden Ansprüche beansprucht, worin der Katalysatorträger einen mittleren Teilchendurchmesser im Bereich von 0,1 pm bis 0,5 cm aufweist. 7. Verfahren, wie in einem der vorstehenden Ansprüche beansprucht, worin der Katalysatorträger eine Oberfläche unterhalb von etwa 20 m2/g aufweist. 8. Verfahren, wie in Anspruch 7 beansprucht, worin der Katalysatorträger eine Oberfläche unter etwa 3 m2/g aufweist. 9. Verfahren, wie in einem der vorstehenden Ansprüche beansprucht, worin das Silber/Gold-Legierung durch Zerstäuben oder lonenplattierung auf den Träger niedergeschlagen wird. 10. Verfahren, wie in einem der vorstehenden Ansprüche beansprucht, worin das sauerstoffhaltige Gas Stickstoff als Trägergas enthält. 11. Verfahren, wie in einem der vorstehenden Ansprüche beansprucht, worin die Reaktion in einem Quarzreaktor durchgeführt wird. 1. Un procédé pour préparer un isocyanate correspondant à la formule où R est un groupe alkyle, un groupe cycloalkyle, un groupe aryle, un groupe aralkyle ou un groupe alkaryle non substitué ne contenant pas plus de 18 atomes de carbone, ou l'un desdits groupes substitué par du chlore, du fluor, le groupe cyano, le groupe alkylcarbonyle ou alcoxycarbonyle dont le groupe alkyle ou alcoxy ne contient pas plus de 10 atomes de carbone, et n est 1 ou 2, qui consiste à mettre en contact un formamide N-monosubstitué correspondant à la formule où R et n sont comme définis ci-dessus, en phase gazeuse avec un gaz contenant de l'oxygène en présence d'un catalyseur constitué d'un support réfractaire dur non poreux en particules sur lequel ont été déposés 0,5­50% en poids d'argent ou d'un alliage argent/or par dépôt physique en phase vapeur. 2. Un procédé tel que revendiqué dans la revendication 1, dans lequel le formamide N-monosubstitué est un composé dans lequel R est -CH3 et n est 1. 3. Un procédé tel que revendiqué dans la revendication 2. qui est effectué à 300―600°C en utilisant un gaz porteur inerte dans lequel 0,1-40 pour cent en volume de monométhylformamide sont présents dans le courant d'alimentation envoyé au réacteur et 0,1-20 pour cent en volume d'oxygène sont présents dans le courant d'alimentation envoyé au réacteur. 4. Un procédé tel que revendiqué dans l'une quelconque des revendications précédentes, dans lequel le support de catalyseur est une matière céramique. 5. Un procédé tel que revendiqué dans la revendication 4, dans lequel le support de catalyseur est de la silice ou de l'alumine. 6. Un procédé tel que revendiqué dans l'une quelconque des revendications précédentes, dans lequel le support de catalyseur a un diamètre de particules moyen compris dans l'intervalle de 0,1 micromètre à 0,5 centimètre. 7. Un procédé tel que revendiqué dans l'une quelconque des revendications précédentes, dans lequel le support de catalyseur a une surface spécifique inférieure à environ 20 mètres carrés par gramme. 8. Un procédé tel que revendiqué dans la revendication 7, dans lequel le support de catalyseur a une surface spécifique inférieure à environ 3 mètres carrés par gramme. 9. Un procédé tel que revendiqué dans l'une quelconque des revendications précédentes, dans lequel l'argent ou l'alliage argent/or est déposé sur le support par pulvérisation cathodique ou implantation ionique. 10. Un procédé tel que revendiqué dans l'une quelconque des revendications précédentes, dans lequel le gaz contenant de l'oxygène contient de l'azote comme gaz porteur. 11. Un procédé tel que revendiqué dans l'une quelconque des revendications précédentes, dans lequel la réaction est conduite dans un réacteur en quartz.